A loudspeaker usually incorporates a loudspeaker driver, which incorporates a movable element which is supported resiliently, and driven to oscillate so as to create a sound wave, and a loudspeaker enclosure to which the loudspeaker driver is mounted. For example the movable element may be driven electromagnetically. In one case, a cone is supported resiliently at its wider end in a support frame, and a driver coil is attached to the narrower and of the cone, the driver coil locating in a magnetic field from a magnet which is also fixed relative to the support frame. By applying varying electrical currents to the coil, the driver coil is caused to move in the magnetic field, and hence the loudspeaker cone oscillates in order to produce sound. Whatever the shape of the movable element, a loudspeaker driver requires a support frame to which the movable element is attached, and the driving means is also fixed relative to the support frame. The shape, material and construction of the loudspeaker enclosure, along with the way in which the loudspeaker driver is mounted to the loudspeaker enclosure, have a strong influence on the quality of sound output by the loudspeaker. A loudspeaker driver is an example of an electro-acoustic transducer. Similar issues arise with other electro-acoustic transducers, such as microphones or headphones.
A particular problem is that the walls of the loudspeaker enclosure tend to vibrate under the influence of the sound produced by the loudspeaker driver. The vibration is particularly noticeable at the resonant frequencies of the walls. Efforts have been made to design loudspeaker enclosures with walls that do not vibrate significantly, or resonate at frequencies outside of the range of sound frequencies produced by the loudspeaker driver. For example, some enclosure designs feature internal bracing to reinforce the walls. Generally, designs that reduce vibration tend to be more complex to build, and are therefore more expensive to manufacture. They can also be relatively heavy, which is particularly disadvantageous for loudspeakers that are intended to be hung, or to be portable. Moreover, whatever the design, some vibrations inevitably persist, leading to a reduction in the quality of the sound output by the loudspeaker.
As regards the driver, a common type of support frame is of cast aluminium, defining a rigid ring to which the movable element is mounted; a rigid end plate to support a magnet; and a number of rigid struts to link the rigid ring to the rigid end plate. Gaps between the rigid struts ensure that the space between the support frame and the movable element is not enclosed. All the elements of the support frame are integral with each other, and are intended to be rigid in order to inhibit vibrations. This has the consequence that they are quite heavy. For example the support frame for a loudspeaker driver of diameter 0.45 m would typically be of cast aluminium, with a mass of about 15 kg.